Table 1.
Characteristics of participants
| Controls (n = 177) | Cases (n = 166) | P | |
|---|---|---|---|
| Age, median (range) at end of follow-up, a y | 10.8 (7.1-15.7) | 12.0 (7.3-15.6)b | <0.01 |
| Female sex | 80 (45.2%) | 81 (48.8%) | 0.51 |
| Preterm birth c | 5 (2.8%) | 10 (6.0%) | 0.15 |
| Cesarean section d | 12 (6.8%) | 28 (16.9%) | <0.01 |
| Parity | 0.42 | ||
| No earlier births | 77 (43.5%) | 83 (50.0%) | |
| 1 | 63 (35.6%) | 49 (29.5%) | |
| 2 or more | 37 (20.9%) | 34 (20.5%) | |
| Maternal age, y, median (range) | 30 (20-42) | 30 (19-42) | 0.29 |
| 19-24 | 24 (13.6%) | 14 (8.4%) | |
| 25-34 | 128 (72.3%) | 130 (78.3%) | |
| 35-42 | 25 (14.1%) | 22 (13.3%) | |
| Maternal smoking during pregnancy e | 0.73 | ||
| Nonsmoker at end of pregnancy | 153 (86.4%) | 143 (86.1%) | |
| Smoked at end of pregnancy | 17 (9.6%) | 18 (10.8%) | |
| Missing data | 7 (4.0%) | 5 (3.0%) | |
| Prepregnancy body mass index, kg/m 2 , median (range) | 22.8 (17.2-40) | 23.9 (15.8-40.5) | <0.01 |
| <25 | 123 (69.5%) | 88 (53.0%) | |
| 25-30 | 27 (15.3%) | 42 (25.3%) | |
| >30 | 15 (8.5%) | 24 (14.5%) | |
| Missing data | 12 (6.8%) | 12 (7.2%) | |
| Child’s HLA genotype f | <0.01 | ||
| Protective (DQ6) | 55 (31.1%) | 4 (2.4%) | |
| Neutral (any other HLA not mentioned) | 29 (16.4%) | 5 (3.0%) | |
| Increased risk (≥1 copy of either DQ8 or DQ2.5) | 70 (39.5%) | 86 (51.8%) | |
| High risk (DQ8/DQ2.5 heterozygote) | 11 (6.2%) | 67 (40.4%) | |
| Missing data | 12 (6.8%) | 4 (2.4%) |
P values from Pearson’s χ 2 test.
a End of follow-up was set as the last diagnosis date of the cases on June 2, 2016.
b Median age of diagnosis was 5.8 (range, 0.7-12.8); only 3 cases were diagnosed after 12 years.
c Defined as birth before pregnancy week 37.
d Includes elective (7 controls, 12 cases) and acute (5 controls, 16 cases) cesarean sections.
e Including those that quit smoking shortly before or during pregnancy because the protective association with type 1 diabetes has been observed in those that smoked throughout pregnancy (49).
f Coded as a binary variable in the analysis—protective or neutral (0) vs increased or high risk (1). The increased risk category (≥1 copy of either DQ8 [DQA1*03-DQB1*03:02-DRB1*04] or DQ2.5 [DQA1*05:01-DQB1*02:01] also required no HLA DQ6 [DQA1*01:02-DQB1*06:02-DRB1*15:01] protective allele).